During the past several years we have been making successful progress in characterizing the mechanical properties of lungs. We wish to continue our efforts during the next several years by applying principles of structural mechanics to study the nature and physiological implications of uneven stresses and deformations in normal and abnormal lungs. Since the last comprehensive progress report submitted in 1975, several important advancements have been made in (1) successful application of the comprehensive finite element model to predict available experimental data on regional lung volumes, (2) experimental validation of the homogeneous and isotropic assumptions, and (3) quantitative predictions for the uneven stresses and strains in the lung as a function of the shape of the chest cavity, the heart cavity and interlobar fissures. Furthermore, we have a clear understanding of the limitations and validities of the various recent efforts on lung elasticity by other investigators. We are in a unique position to more rigorously advance the analytical and experimental approaches to further quantify the uneveness of the lung parenchyma and its physiological and pathological implications. More specifically, we intend to study the local responses when material properties are different, (e.g., airway vs. parenchyma, parenchyma continuum contains a region of diseased tissue, interaction of heart and lung parenchyma, etc.) as well as the gross lung behavior by including the chestwall and the abdomen in order to compare with the many available experimental data of chestwall mechanics studies. Experimental studies will be carried out when material properties or special experimental validation becomes necessary.